Then my iMac decided that it was going to indulge in some image persistence (the LCD answer to phosphor burn-in) from Firefox. I've disabled the parts of the FF window that were causing it, and I'll be running screen-savers of either all-white or scintillating colors for the foreseeable future. Grumble grumble, gripe gripe!
Ah well, at least I'm not on fire.